Heretofore, it has been considered to be very difficult to form a narrow tissue fistula having an internal diameter of, for example, 6 mm or less in a living body, etc. In particular, there has been no technique for forming a tissue fistula having an internal diameter of 3 mm or less. However, there are several known methods for forming a comparatively wider tissue fistula, and methods using a mandril are also known. Specific examples of known methods of forming a fistula by inserting a (comparatively thick) mandril, may include a method wherein cells are attached outside a living body, and a technique for attaching cells in a living body.
A typical example of the technique for the method of forming a tissue in a living body is U.S. Pat. No. 3,710,777 filed by Sparkes. In this technique, a metal pipe is inserted in coincidence with the location where a blood vessel implantation is to be performed in advance within the subcutaneous tissue of the thigh in a patient with an occluded femoral artery, and a combination wherein an artificial blood vessel made of Dacron fabric (trade name, polyester fiber, Dupont) is covered around the outside of a silicone rod having an outer diameter of 6-8 mm, is inserted within the pipe, and then only the metal pipe is extracted therefrom. As a result, the combination of a silicone rod and fabric artificial blood vessel is allowed to remain in the subcutaneous tissue in the site where the blood vessel implantation is to be performed.
In this manner, when the silicone rod is removed after a predetermined time period (e.g., 3 months) has elapsed, since cells are entangled with the fabric artificial blood vessel, a tissue fistula is formed wherein the fibers of the fabric artificial blood vessel serve as a framework at the location where the blood vessel implantation is to be performed on the patient. U.S. Pat. No. 3,710,777 discloses such a technique wherein an artificially formed tube is used as an artificial blood vessel in the site of the patient's own occluded femoral artery.
The above-mentioned Sparkes technique is commercially available under the name of the Sparkes mandril graft, and is widely used clinically. However, when this type of mandril graft is actually used, tissue formation in a living body does not proceed as would be expected, and the mandril must be inserted in a living body for a period of at least three months in order to obtain reliable tissue formation. In addition, the adherence of cells to the fibers of the fabric is poor, even in the case of the insertion into a living body for such a long period of time. Further, since the tissue formation tends to be incomplete at the portion which contacts with the silicon rod on the inside of the Dacron fabric in particular, the above product has been reported to be unable to fulfill the function of an artificial blood vessel (see Hallin R W, Sweetman W R: The Sparkes' Mandril Graft—A seven year follow-up of mandril grafts placed by Charles H. Sparkes and his associates, American Journal of Surgery, 132; 221-223, 1976). In consideration of these circumstances, the Sparkes mandril graft was gradually used less and is currently not used at all.
In the above-mentioned Sparkes technique, a silicone rod is placed in contact with the luminal surface of the above-mentioned Dacron (polyester fiber) fabric, and is inserted into a living body. According to the approach adopted by Sparkes, cells are expected to infiltrate into the interstices between the fibers of the Dacron fabric. However, as the Dacron fibers are coated with silicone and the coated silicone is present in contact with the Dacron fibers, the infiltration and migration into the interstices of the physiologically inactive silicone as well as mitosis and other cell activities are inhibited, and the circulation of body fluid, for supply of nutrition to the cells, is also impaired. That is, the prolonged presence of the silicone in a living body impaired the tissue formation at the portion in contact with the silicone because it is a non-physiological substance.
Such non-physiological substances are typically surrounded by a tissue containing large amount of collagen fibers generally referred to as scar tissue. In pathological terms, this is referred to as “encapsulation”. Accordingly, in the case of the Sparkes technique, the rich collagen tissue is formed due to this encapsulation phenomenon, and it is extremely rare for cells to be exposed on the surface thereof.
Moreover, in the Sparkes technique, the above-mentioned Dacron (polyester fiber) artificial blood vessel is essential. A tissue fistula is formed as a result of cells adhering to these Dacron fibers. Accordingly, the presence of these Dacron fibers is essential.
As a technique for forming tissue in a living body is considered to be theoretically superior for the growth and migration of cells in a living body, attempts have been repeated by using new techniques. A typical example of such an attempt is disclosed in U.S. Pat. No. 5,171,261, which describes an effective technique for slicing tissue into thin sections, and disseminating the resultant tissue sections so as to implant them in the form of an artificial blood vessel. In addition, other techniques have also been developed for forming vascular-like tissue in a living body as disclosed in U.S. Pat. Nos. 5,849,036 and 5,399,352.
Auxiliary techniques for forming a fistula in a living body in regions other than blood vessels may be used for preserving the form of a fistula for treatment of constriction of the nasolacrimal duct. Examples of the prior art relating to these techniques include U.S. Pat. Nos. 6,238,370, 6,082,362, 5,423,777, 4,959,048 and 4,380,239.
Other examples include techniques used for the bile duct and during constriction of the esophagus, and such techniques are described in U.S. Pat. Nos. 5,716,981 and 5,120,322. However, these techniques do not intentionally form a narrow fistula by using surrounding cells.
An extremely large number of examples of the prior art have been reported and relate to filamentous substances which are degraded and absorbed in a living body. These techniques were reported a long time ago as is evidenced by, for example, U.S. Pat. No. 3,976,071. Moreover, there are numerous other examples of this technique, including U.S. Pat. Nos. 5,010,145, 6,063,117 and 5,584,836. Moreover, examples of prior art simultaneously using a cell growth factor and cells, etc., include U.S. Pat. Nos. 5,386,012 and 5,885,829, while U.S. Pat. No. 5,614,515 reports a technique used for the purpose of preventing adherence.
Although there are several other techniques which are used in the form of fibers or filaments using substances which are degraded and absorbed in a living body, there has been no technique for forming a fistula within various organs and tissues, nor a technique which uses such a technique to form various types of tissue fistula (namely, technique for forming and inducing artificial tissue fistula).